The present invention relates generally to a variable valve apparatus or system for internal combustion engine, and more particularly to a variable valve apparatus which has a valve lift adjusting mechanism for adjusting a valve operating characteristic of an engine valve set of an internal combustion engine independently of other engine valve sets of the engine.
Japanese Published Patent Application No. 2001-123809 (hereinbelow referred to as “JP2001-123809”) shows such a variable valve apparatus for internal combustion engine. The variable valve apparatus of JP2001-123809 is adapted for internal combustion engines having a plurality of cylinders such as four-cylinder internal combustion engines and six-cylinder internal combustion engines. The variable valve apparatus of JP2001-123809 generally comprises: a drive shaft rotating in synchronization with a crankshaft; a drive cam provided for each cylinder and attached to the drive shaft with eccentricity to the axis of the drive shaft; two swing cams provided for each cylinder and adapted for opening and closing two intake valves of each cylinder; and a multi-articulated power transmitting mechanism provided for each cylinder and adapted for converting the eccentric rotary motion of the drive cam into a swinging motion of the swing cams. The power transmitting mechanism comprises: a rocker arm located above the swing cams and supported for swinging motion on a control shaft; a link arm linking the drive cams and one wing portion of the rocker arm; a link rod linking the swing cams and the other wing portion of the rocker arm. Specifically, the control shaft is formed as a straight member extending in the longitudinal direction of the engine, and is rotatably supported on bearings provided on an upper end of a cylinder head of the engine. The control cam is formed on the outer peripheral surface of the control shaft for each cylinder, and is adapted to serve as an axis of rotation of the swinging motion of the rocker arm. When the rotational position of each control cam is changed via the control shaft by an actuator in accordance with engine operating conditions, the axis of rotation of each rocker arm moves to vary the lift height of each intake valve. As constructed above, the foregoing variable valve apparatus comprises many parts including the many parts of the multi-articulated power transmitting mechanism. As a result, errors in machining and assembling tend to cause variations in the lift height among intake valves, especially to cause variations in the valve lift height among cylinders. In order to solve this problem, the variable valve apparatus of JP2001-123809 includes a valve lift adjusting mechanism for making an adjustment to the lift height of each intake valve. The valve lift adjusting mechanism is provided for every valve actuating mechanism comprising the above-mentioned power transmitting mechanism, or for every cylinder.